This invention relates to long path gas absorption cells for spectrographic analysis, particularly those that can be utilized in existing spectrophotometers employing frustrated total internal reflection in elongated rods having conical end faces. Instruments of this type are disclosed in my prior U.S. Pat. No. 3,370,502, Issued: Feb. 27, 1968, entitled FRUSTRATED MULTIPLE INTERNAL REFLECTION ROD WITH VARIABLE LENGTH FLUID CONTAINING ENCLOSURE MEANS; and U.S. Pat. No. 3,460,893, Issued: Aug. 12, 1969, entitled APPARATUS FOR ANALYZING A CONTINUOUSLY MOVING STRIP BY MEANS OF ATENUATED TOTAL INTERNAL REFLECTION; and, in particular, in my British Patent No. 2,105,058, granted Jan. 8, 1986 entitled FRUSTRATED MULTIPLE TOTAL INTERNAL REFLECTION ABSORPTION SPECTROPHOTOMETER. Another form of optical system, in which my new gas cell may be employed, is a spectrophotometer employing reflaxicon optics and also using a rod with conical end faces disclosed in U.S. Pat. No. 4,595,833 of Donald W. Sting, Issued: Jun. 17, 1986 for MULTIPLE INTERNAL REFLECTION CELL OPTICAL SYSTEM FOR USE IN INFRA-RED SPECTROPHOTOMETERY OF LIQUID AND FLUIDIZED SAMPLES.
Instruments according to both of these latter patents, are available from Spectra-Tech, Inc., Stamford, Conn. U.S.A. under the Trademark The Circle.TM..
Instruments according to my above-identified British Patent, are available from General Analysis Corporation, South Norwalk, Conn., U.S.A. under the Trademark LAN.TM..
The gas cell of the present invention is designed to be directly substituted for the conical end face frustrated total internal reflection liquid sampling rod and cell used in the above-identified instruments.
As these instruments employ cells of relatively short lengths, in the order of 1 to 3 inches, traditional gas
cells employing light pipes--that is very long, thin cylinders--do not provide sufficient absorption in these instruments for many applications